1. Field of the Invention
The invention pertains to a shaped part with a spigot for connecting to a tube, while the spigot has several troughs arranged in the direction of its longitudinal axis. The invention is applicable to the field of assembly technology, especially in the area of automotive technology and thereto windshield wiper equipment.
2. Description of the Art
Windshield wiper assemblies for automobiles are often of modular design. Each wiper bearing is equipped with a spigot which is fixed in a carrier designed as a tube. The tube connects the wiper bearing to the wiper motor. The attachment of the tube to the spigot is accomplished by plastic deformation of the tube, which is also called crimping. The crimping ensures that forces and moments can be coupled between the spigot and the tube.
A windshield wiper assembly with a tubular carrier that is affixed to a tab or a spigot of a wiper bearing is known from DE 2 920 899. The spigot has four trough-like recesses at right angles to its longitudinal axis, two of which are always oppositely arranged. Carrier material is forced into the recesses by means of a plunger, which is designed to complement the recess form that makes contact with the entire recessed area of the spigot.
In the case of the known wiper assembly, the union between the spigot and the tube may separate during the transfer of forces and moments. This may especially be the case when great temperature fluctuations are involved, such as temperatures ranging from xe2x88x92400xc2x0 C. to +1,200xc2x0 C. However, separation of the connection may also occur with lengthy constant operation of the windshield wiper assembly or when the wiper is blocked, for example, by snow or ice. Separation of the connection between the spigot and the tube results in unacceptable loud noise when the wiper assembly is operated.
Accordingly, the problem fundamental to the invention is one of making available a shaped part with a spigot that overcomes the aforesaid disadvantages. In particular, separation of the connection between the spigot and the tube should be precluded even under marginally extreme conditions.
The problem is solved by the shaped part disclosed in the independent Patent Claim. Special embodiment forms of the invention are disclosed in the subordinate claims.
The problem is solved by a shaped part with a spigot designed for joining to a tube, wherein the spigot has several troughs arranged in the direction of its longitudinal axis, in each case two adjoining troughs are separated by two projections extending at right angles to the longitudinal axis of the spigot. Within the framework of the present invention, an FEM calculation of the solution described above has shown that the type and the degree of the forming operation has a great influence on the instabilities of the crimping. In the known technique, full plastification is not attained in some crimp areas. This results in high residual tensions after release of the tool. These tensions develop into compressive stresses and, under external strains, form an unstable tension state in the tubular piece and cause further deviation from the normal contour. The contact surfaces between the spigot and the tube are not adequately constructed which can lead to a separation of the union. Characteristic of the invention by virtue of the separation of the troughs by the projections and prior to the release of the tool, the compressive stresses are surrounded by tensile stresses that are greater than the compressive stresses. These tension differences and distributions based on the geometry of the troughs are advantageous, as the stresses are reversed after release of the tool. This means that the tensile forces are converted into compressive forces, i.e., in the direction of the interior of the trough, and the compressive forces are converted into tensile forces, i.e., away from the core. The stronger tensile forces act against the enclosed compressive forces and result in a good, homogeneous distribution of the compressive stress on the core. Thereby a stable crimping in the trough area is realized.
A special embodiment of the invention is characterized in that each of the projections has two projection wings that extend out from the edges of the trough and are first concavely and then convexly curved. The concave/convex transitions of the projections act counter to axial stresses. With these transitions, a xe2x80x9cclutchingxe2x80x9d of the material of the tube around the spigot results. This effect is realized by opposing compressive forces in the concave areas. By means of the convex transitions, a stable equilibrium is achieved.
Another special embodiment form of the invention is characterized in that the spigot has at least three troughs and that an inversion snub is located in the middle trough of the three troughs. The inversion snub ensures a better stability of the middle trough and thus makes possible a homogenization of the stress distribution in the base. As a result, the base area does not lift away from the spigot when the tool is released.
Yet another special embodiment form of the invention is characterized in that the troughs are located on opposite sides of the circumference of the spigot. An especially secure seating of the tube on the spigot is thereby achieved.
The precept of the present invention also encompasses a process for connecting the shaped part described above to a tube, which is characterized by the following steps: the tube is slipped over the spigot; the tube together with the spigot is placed into a double-action tool with two crimpers; the tool is closed in such a way that it encircles the tube, while the spigot is fixed relative to the tool by the grasping hole, and the two crimpers are brought together; the tube is plastically deformed, surrounds the spigot, and assumes the geometry of the spigot or the crimpers in the area of the deformation zone.
The technical advantage of a union of a tube with a spigot by this process lies in the fact that an almost stress-free state of equilibrium is established in the tube. This means that no unstable condition of stress develops due to external strains that might lead in turn to separation of the connection.
The solution according to the invention results in adequate plastification, i.e., a good flow of material and concurrently a good strengthening is achieved. Sufficient contact zones and stable stress conditions are thereby realized.